Washington: A pattern of disturbed sleep could be an early warning sign of Alzheimer's disease, suggest scientists.

Working on a mouse model, researchers from the Washington University School of Medicine in St. Louis, found that when the first signs of Alzheimer's plaques appear in the brain, the normal sleep-wake cycle is significantly disrupted.

"If sleep abnormalities begin this early in the course of human Alzheimer's disease, those changes could provide us with an easily detectable sign of pathology," said senior study author David M. Holtzman, professor and head of neurology at Washington, the journal Science Translational Medicine reported.

"As we start to treat Alzheimer's patients before the onset of dementia, the presence or absence of sleep problems may be a rapid indicator of whether the new treatments are succeeding," added Holtzman.

Holtzman's lab was among the first to link sleep problems and Alzheimer's through studies of sleep in mice genetically altered to develop Alzheimer's plaques as they age, according to a university statement.

In a 2009 study, he showed that brain levels of a primary component of the plaques naturally rise when healthy young mice are awake and drop after they go to sleep. Depriving the mice of sleep disrupted this cycle and accelerated the development of brain plaques.

A similar rising and falling of the plaque component, a protein called amyloid beta, was later detected in the cerebrospinal fluid of healthy humans studied by co-author Randall Bateman, professor of neurology at Washington University.

The new research, led by Jee Hoon Roh, neurologist and postdoctoral fellow in Holtzman's lab, shows that when the first indicators of brain plaques appear, the natural fluctuations in amyloid beta levels stop in both mice and humans.

Mice are nocturnal animals and normally sleep for 40 minutes during every hour of daylight, but when Alzheimer's plaques began forming in their brains, their average sleep times dropped to 30 minutes per hour.